Effects of perfusion pressure on Ca2+ sparks in rat renal afferent arterioles

Abstract

Mechanical force can be transduced into freshly isolated renal vascular smooth muscle cells (VSMCs) to trigger Ca2+ sparks. Sparks can trigger Spontaneous Transient Inward Currents (STICs), and regulate myogenic tone via membrane depolarization. Electrophysiological studies indicate the presence of STICs in isolated renal VSMCs. Hence, we sought to determine whether the occurrence of Ca2+ sparks is increased during pressure induced myogenic constriction. Line scan images were collected from perfused rat afferent arterioles at 500 Hz using laser scanning confocal microscopy. We detected spontaneous Ca2+ sparks in 40% of the VSMCs at a perfusion pressure of 80 mm Hg. These sparks were suppressed by 50 μM ryanodine and were augmented by 0.5 mM caffeine. The mean spontaneous Ca2+ spark frequencies were 0.14±0.04 sparks/s (n=23 cells) and 0.24±0.11 sparks/s (n=13 cells) at 80 mm Hg and 120 mm Hg, respectively. These suggest that the increase in frequency of sparks is probably related to pressure induced myogenic constriction. Intriguingly, the frequency of Ca2+ sparks observed in SHR afferent arteriole was double compared to that of normotensive rats at the same perfusion pressure. These observations implicate that the enhanced Ca2+ sparks frequency may contribute to the increase of renal vascular resistance in SHR.